We've used priceline before and not had any issues. However, I would only try priceline within a week or so of travel. IMO, the main downside of priceline is that you may not get a free driver. So I always factor in savings, vs if I do a traditional rental and know the spouse is free. The other downside is that you can't precheckin on line or go right to the garage. For most of our rentals the past several years, I have been able to use codes and coupons and get a price less than the hotwire price. That doesn't seem to be the case this fall, although prices do seem to be coming down. April 2007, I did priceline about a month before our travel days. Then about a week before I could have booked NAtional EA for the same price.
Keep in mind with priceline, If you have to cancel for any reason, there's not refunds.
$8 is a great price! Enjoy!